Impact of Body Mass Index on All-Cause Mortality in Adults: A Systematic Review and Meta-Analysis

Background: Obesity is a risk factor for many diseases, diagnosed by calculating body mass index (BMI). Methods: To find an association between BMI and mortality in adults, we searched PubMed for articles published in the 21st century. Our review included 82 original studies, comprising 2.7 million patients and 23.4 million patient years. Results: The meta-analysis showed a U-shaped relationship between BMI and all-cause mortality risk, with the lowest mortality in the BMI range of 25-30 kg/m². Subgroup analysis showed a J-shaped relationship, with greater risk in the highest BMI range (>35 kg/m²). Among the elderly, BMI values <20 kg/m² were associated with the highest risk. Among diabetic patients, a U-shaped relationship was noticed, again with the highest risk in the lowest (<20 kg/m²) and highest BMI range (>35 kg/m²). Among patients with cardiovascular disease, the risk increased with BMI values <25 kg/m² but did not noticeably change for BMI exceeding that value. Among cancer patients, the relationship was less pronounced than in other subgroups, with a slightly higher risk (>35 kg/m²). Conclusions: Our results show that the lowest mortality is observed among patients with BMI 25-30 kg/m². Reduction of body mass should not be a universal recommendation in clinical practice, but it should be individualized.